Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. Emulsion aggregation toners may be used in forming electrophotographic images. Emulsion aggregation techniques may involve the formation of a polymer emulsion by heating a monomer and undertaking batch or semi-continuous emulsion polymerization, as disclosed in, for example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,902,710; 5,910,387; 5,916,725; 5,919,595; 5,925,488, 5,977,210, 5,994,020, and U.S. Patent Application Publication No. 2008/0107989, the disclosures of each of which are hereby incorporated by reference in their entirety.
Polyester toners have been prepared utilizing amorphous and crystalline polyester resins as illustrated, for example, in U.S. Patent Application Publication No. 2008/0153027, the disclosure of which is hereby incorporated by reference in its entirety. The incorporation of these polyesters into the toner requires that they first be formulated into emulsions prepared by solvent containing batch processes, for example solvent flash emulsification and/or solvent-based phase inversion emulsification (PIE), which are both time and energy-consuming. In both cases, large amounts of organic solvents, such as ketones or alcohols, have been used to dissolve the resins, which may require subsequent energy intensive distillation to form the latexes, and are not environmentally friendly.
These batch processes may be difficult to scale-up, since the process inputs (i.e. resin acid value) can vary and there are many possible noise variables (i.e. solvent evaporation, NH3 evaporation). For example, variation in the lot-to-lot resin acid value may require different process input variations (i.e. neutralization ratio, solvent ratio) to achieve the desired particle size and may require extensive work before a resin lot is scaled-up. Moreover, it may still produce failed batches. In addition to poor mixing properties, the individual batch process involves the handling of bulk amounts of materials, and each process may take many hours to complete before moving to the next process in the formation of the toner, that is, aggregation and/or coalescence. In addition, batch-to-batch consistency is frequently difficult to achieve because of variations that may arise from one batch to another.
Solventless latex emulsions have been formed in either a batch or extrusion process through the addition of a neutralizing solution, a surfactant solution and water to a thermally softened resin as illustrated, for example, in U.S. Patent Application Publications Serial Nos. 2009/0246680 and 2009/0208864 the disclosures of each of which are hereby incorporated by reference in their entirety. However, a small amount of coarse material often remains un-emulsified in these processes and so the conversion of the resin to the latex may not be complete. The latexes therefore may be treated to remove this coarse content, or a polishing step may be added to convert the residual resin or coarse material into latex particles. For example filtration may be used to remove any coarse material, while ultrasonication and/or homogenization using external high shear devices may be applied to the latex produced from the extruder to complete the conversion. These additional process steps are, however, not desirable as they add complexity, energy consumption and cost. Additionally, conventional processes have limited applicability with respect to the choice of polyester resin. In particular, certain resins degrade during the process based on their molecular weight and composition, leading to latexes with polymers of lower molecular weight than the starting material. While not wishing to be bound by theory, the polyester degradation is thought to be the result of base-induced hydrolysis of the polyester backbone.
It would be advantageous to provide a process for the preparation of a polymer latex suitable for use in a toner that is more efficient, takes less time, and has a high product yield.